Switch contact element



June 4, 1957 F, MORSE 2,794,888

SWITCH CONTACT ELEMENT Filed June 28, 1956 INV TOR. F0255 0/655 United States Patent SWITCH CONTACT ELEMENT Forbes Morse, Manhasset, N. Y.

Application June 28, 1956, Serial No. 594,436

Claims. (Cl. 200-166) The present invention relates to electrical circuit making and breaking devices and, more particularly, to a switch contact element or brush adapted for use in connection with analogue to digital converters and othe switching devices.

In such devices, a disc, having electrically conductive and non-conductive segments, rotates with respect to an assembly having a support or deck carrying one or more contact elements or brushes which engage the disc and control the energization of electro-devices arranged in circuits therewith. It is very important that the on and off periods be accurately timed and in some instances be of very nearly equal duration. To achieve this, a predictable, uniform and efiective brush-width must be provided.

Heretofore, attempts have been made to provide such switching equipment, but extensive tests revealed that the duration of the desired periods deviated slightly more than 2%. While it has been possible to correct for such deviations, this could only be accomplished by numerous calculations and the use of conductive segments having odd dimensions which introduced manufacturing difiiculties and increased fabricating costs. Also, in attempting to solve these prior ditficulties, contact elements have been devised which, while providing better timing accuracy, scraped or gouged the disc sections engaged thereby, thus greatly shortening the useful life of such switching devices.

Accordingly, an object of the present invention is to provide a novel and improved switch contact element or brush adapted for use in connection with such devices, which element provides for more accurate and exact timing of the on and off periods, and does not inflict damage to the disc sections engaged thereby.

Another object is to provide such a switch contact element which is simple and economical to manufacture and to install, and which does not complicate the design and manufacture of the instrument in which it is used.

A further object is to provide such a switch contact element which, while of a delicate nature, is sufiiciently rugged by reason of its design to withstand the usage to which it is subjected.

Other and further objects will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the inven tion in practice.

In accordance with the present invention, the foregoing objects are accomplished by providing a contact element comprising a fine wire which is formed with an off-set, U-shaped portion, the base of the U being reduced in thickness, thereby providing a contact face of substantially uniform cross-section as it wears during its engagement with the disc. In order to increase the flexibility and the lateral stability of the contact element, the said wire is preferably bent upon itself to provide two legs extending from said off-set portion, and these legs are flattened for a considerable length thereof.

A preferred embodiment of the invention has been chosen for purposes of illustration and description and is shown in the accompanying drawing, forming a part of the specification, wherein:

Fig. 1 is a top view of the assembly for mounting the contact element.

Fig. 2 is a sectional view, taken along the line 2-2 on Fig. 1, illustrating the contact element and its mounting assembly, as seen from one side thereof.

Fig. 3 is a bottom plan view, taken along the line 33 on Fig. 2, illustrating the contact element and its mounting assembly.

Fig. 4 is an enlarged side view of the portion of the contact element provided with the contact face.

Referring in detail to Figs. 1 to 3 of the drawing, a contact element 10 is illustrated, as used in a switching device, wherein a disc 11, having a conductive section 12 and non-conductive sections 13 is arranged for relative movement with reference to a deck 14 carrying a mounting assembly or slider 15 to which the contact element It) is rigidly secured.

By way of example, as illustrated herein, the mounting assembly 15 comprises a brush support 16 of conductive material having a threaded tubular upwardly extending formation 17, and being mounted beneath a slot 18 in the deck 14 by means of a washer 19 of greater diameter than the width of the slot 19 and a screw 20 extending through the washer 19 and threaded into the formation 17. One end 21 of the brush support 16 is reduced in width and extends upwardly into the slot 18 in the deck 14; and to this end 21 a conductor of electricity (not shown) is connected. The other end of the brush support 16 is likewise reduced in width and has a depending leg 22 formed with a foot 23 at its free end. The brush support 16 is also provided with an upstanding portion 21 which extends upwardly into the slot 13 in the deck 14.

In accordance with the present invention and, as shown more particularly in Figs. 2 to 4, the contact element or brush 10 comprises a wire member of relatively small diameter, which member is bent upon itself to provide two identical diverging legs 24 secured at their free ends to the foot 23 of the brush support 16 by brazing, soldering or welding. At the end opposite the free ends of the legs 24, there is formed an offset, U-shaped portion 25 which interconnects the legs 24 and depends therefrom. The base of the U is reduced in thickness, for example by flattening the same, at the outer or exposed sides 26 thereof to provide a contact face 27 for engaging the sections 12 and 13 of the disc 11.

It will be noted that the contact face 27 is arcuate in cross-section by reason of the roundness of the wire member from which it was formed. Thus, for example, if the disc 11 moves from left to right with respect to the member 14, as viewed in Fig. 2, the flat surfaces of the sections 12 and 13 move tangentially with respect to the arc of the contact face 27, whereby the contact face 27 does not present any sharp edges which might inflict damage to or induce excessive wear of the sections 12 and 13 of the disc 11. By reason of the tangential contact zone of infinitesimal thickness the change from on to off, or vice versa, is instantaneous and can be accurately predetermined by the positioning of the contact element with respect to the disc sections. Furthermore, the flattening of the contact surfaces 26 provide a configuration that maintains uniform brush width even after considerable wear-down of the contact face 27.

The portions of the legs 24 extending from the free ends thereof almost to the off-set portion 25 preferably are flattened in planes parallel to the surface of the disc 11, as shown at 28 in Figs. 3 and 4. This increases the flexibility and lateral stability of the legs 24-toprovide-- for light but positive pressure of the contact face 27 on the disc sections 12 and 13, and facilitates securement of the legs 24 to the foot 23" of the brush support 16 'by enabling a connection-tobe formed between 'flat abutting surfaces. The parts of the legs and-the off-set portion,

which are unaltered and remain cylindrical, provide a desired rigidity at the contact end 27 of the element-andthereby prevents distortion thereof.

The contact element or brushltl is preferably of a palladium silver alloy or a material having similar properties. Palladium-silver alloys are suitable because they are compatible with other metals or'alloys, have good spring qualities, are sufficiently ductile to-facilitate forming operations, have good wearing qualities, and are hardenable by heat treatment.

In a practical embodiment of the presentinvention, the dimensions of the brush element'preferably areapproximately in the following proportions:

Diameter of wire .010 inch. Overall length of legs 24 .470 inch. Length of flattened portions 28 .370 inch. Thickness of flattened portions 28 .003-.004 inch. Length of off-set portion 25 .050 inch. Thickness of U at 26 .004.005 inch. Space between legs 24 of U .006.012 inch.

Angle of off-set portions 25 to legs 24 90 :5,.

Brush elements somewhat larger or smaller in size achieve the advantages of the present invention whenconstructed in such proportions; for example, the reduction in thickness of the U at 26 is about one-half the diameter of the wire employed.

From the foregoing description, it will be seen that the present inventionprovides an improved contact element or brush for delicate switching devices wherein the timing accuracy is of utmost importance. These elements are made in a simple, practical and economical manner and can withstand any usage to which they may be normally subjected.

As various changes may be made in the form construction, and arrangementof theparts herein, without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matters are to be interpreted as illustrative and not in any limiting sense.

What is claimed is:

l. A switch contact element of fine wire formed with an off-set, U-shaped portion, the base of said U-shaped portion being reduced in thickness, thereby providing a contact face of substantially uniform Width as it wears.

2. A contact element according to claim 1, wherein said wire is bent upon-itself to provide two legs extending from said off-set portion.

3. A contact element according to claim 2, wherein a portion of each of said legs is flattened, thereby increasing the flexibility and lateral stability of the contact element.

4. A switch contact element comprising a wire member of relatively small diameter bent upon itself to provide two diverging legs and being formed with an off-set, U-shaped portion connecting the legs, the base of the U being flattened at the exposed sides thereof to provide a contact face having an .arcuate cross'section, the free ends of the legs being flattened in the direction in which the off-set portion extends, thereby increasing the-flexibility and lateral stabilitythereof.

5. A switch contact element according to claim 4, wherein the wire member is formed of a palladium-silver alloy having a diameter of about 0.01 inch, the overall length of the legsis about 0.47 inch and the flattened portion thereof has a length of about 0.37 inch and a thickness of between about 0.003 and 0.004 inch, the off-set portion has a length of about 0.05 inch and is at about a right angle to the legs, and the flattened portion of the case of the U has a thickness of about between 0.004 and 0.005 inch.

No references cited. 

